The instant invention relates to plugs used to seal the fluid ports of an engine block.
The prior art teaches the use of freeze plugs comprised of a solid piece of metal, wood or plastic typically having an outer surface formed in the shape of a conical frustum. The port is sealed by forcibly inserting the plug therein. As the fluid contained within the engine block begins to expand upon freezing, the plug is dislodged from the port by the increased pressure incident to such expansion, and the freezing fluid is able to escape the confines of the engine block, thereby avoiding engine block damage. Unfortunately, the pressure at which the plug is forced from the port cannot be consistently predicted, since the installation of the plug damages the mating surfaces of both the plug and the engine block port, thereby providing an indeterminate additional amount of frictional contact therebetween. The force due to the frictional contact is exacerbated at temperature extremes by the disparity in the coefficients of thermal expansion for the engine block and plug materials.
Alternatively, the prior art teaches the use of pipe plugs comprising a solid element characteristically formed of metal having an externally threaded surface. The pipe plug is threadably inserted into an engine block port that has been tapped to receive the threaded portion of the plug, whereby the port is sealed. The pipe plug must be carefully advanced into the engine block so as to avoid damage thereto from overtightening. Cross-threading is frequently encountered, and irreparable damage to the engine block is not uncommon, where the plug is formed of a harder material than the engine block, such as the use of an iron plug in an aluminum block and where the plugs are inserted and advanced by machine. Moreover, sealant applied to the threaded portion of the pipe plug is frequently removed during automated insertion thereof into the engine block port, thereby generating leak paths that reduce seal effectiveness.